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Hi,

I am simulating insteady flood waves in a river. Now I have the problem, that I have several areas in the model, where an outflow has been calculated but the surface of the river is not reaching the top of the levee. The water in Telemac is more or less flowing up the levee and down on the other side. See Screenshots.

Has anybody a hint?

Thanks,
Gabi

Hello Gabi

This is likely what we call "the numerical pumping" which is caused by the compibed effects of the wetting/drying algorithm of Telemac and the existence of dikes loosely discretized.
The solution can be :
1- add the keyword THRESHOLD DEPTH FOR RECEDING PROCEDURE (in meter) which will trigger the receding of water when this latter goes upper than this threshold.
2- remesh the dyke locations in a way that includes at least 5 nodes per section with a chineese hat shape.
You will find more details in user manual at section 3.2.16.1.

I hope that this helps

with my best regards

Riadh ATA

Hi Riadh,

thanks for the answer, I hoped to prevent option 2 .....
Remeshing 60km river Banks is not my favourite option, but it may be the Price for using an existing SMS mesh.

Many thanks,
Gabi

Hello,
I have the same problem of overtopping a levee, despite i added the keyword THRESHOLD DEPTH FOR RECEDING PROCEDURE to 0.1

The levee is meshed by two nodes on the top







I work with V6P3.

Thanks.

Hello,

Yes, with 2 points for describing the levee it is a desperate case, a spurious depth on the levee, due to the influence of the deep water in a neighbour point, tend to flow on the other side. This is why we advise to discretise a levee with more points. You can try :

OPTION DE SUPG : 0;0

and/or:

TRAITEMENT DES HAUTEURS NEGATIVES : 2

it could mitigate a bit the problem (not sure).

If the wrongly flooded area will never be flooded you can also change its bottom topography...

With best regards,

Jean-Michel Hervouet

Not better with this two options.
So, i will try to add more points on the upstream face of the levee

Thank you for your help!

Hello,
I discetised the levee with more points (mesh under 1m) but i have already the same problem :








Perhaps something is wrong in my case file ?

Hello,

Well the refinement is not optimal, you still have one point in the water which is a neighbour of one point at the top of the levee, and then the top is all flat, so water can flow back on the wrong side. You would need one or 2 dry points on the slope of the levee. Maybe this can be done without adding new points, just by changing the elevation of 2 of the 5 points at the top so that they are at mid-slope. The difficulty in this case for the algorithms is to make the difference between a real overtopping (e.g. a wave striking the levee) and a fake overtopping due to discretisation errors.

With best regards,

Jean-Michel Hervouet